1. Field of the Invention
This invention relates to direct current conversion to different voltage levels and, more particularly, to bilateral dc-to-dc converters.
2. Description of the Prior Art
It is often desirable to power electrical systems from a remote location in order to avoid the difficulty of generating or locating a local source of electrical energy. Telephone subscriber loop systems, for example, are most advantageously powered from the telephone central office over the telephone wires to reduce the dependence of telephone service on outside power sources. The electrical resistance of the telephone wires, however, limits the amount of power which can be made available at long distances from the central office.
The power available at the remote terminals of a long telephone loop can be increased by charging a remote battery when power requirements are low and then operating from the battery for higher power demands. Voltages currently being applied to telephone pairs, however, are traditionally in the range of 130 to 270 volts while the voltage levels necessary to power semiconductor circuits are usually less than 20 volts. This suggests the need for direct current voltage level conversion in such systems.
One difficulty with powering remote electronics from a local battery is that power can be supplied only at a single remote point. If the electronics are distributed along the subscriber loop pair, high-to-low level converters must likewise be located along with the loads. Ideally, the remote battery should be at the same voltage level as the central office supply to permit direct charging and at the same time to supply power anywhere along the loop. Batteries at such high voltage levels, however, are expensive because they require a large number of cells to achieve the required voltage level.